Enhanced Removal of Pharmaceutical Contaminants from Water Using Electrochemical Oxidation Coupled with Adsorption Process
No Thumbnail Available
Date
2024-05
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
Pharmaceutical contaminants are emerging water contaminants that have become a growing global concern. These contaminants have been frequently detected in surface water, wastewater and drinking water at trace concentrations. Among the pharmaceuticals, acetaminophen (ACM) and ciprofloxacin (CIP) are extensively consumed as analgesics and antibiotics, respectively, and thus ubiquitously detected in the environment. These contaminants are associated with negative effects on human health and aquatic life. In response to this problem, treatment processes such as electrochemical oxidation (EO) and adsorption have previously been attempted as single treatment systems to remove these pharmaceuticals from water. However, these single treatment systems are highly sensitive to water matrix, and their efficiency is limited when employed in multiple pharmaceuticals removal from complex water matrices. Therefore, this study aimed to elucidate the performance of individual (EO and adsorption) and coupled processes (EO+adsorption) in the removal of these pharmaceuticals from water to investigate the benefit of coupling both processes. The individual EO and adsorption processes were independently optimized and then compared with the EO+adsorption process. The adsorption process was conducted using a chemically activated carbon (CAC) synthesized from bamboo sawdust. The comprehensive CAC characterization results, such as BET surface area, SEM, FTIR, Raman spectroscopy and pHpzc, showcased its remarkable adsorptive properties (high surface area, plentiful functional groups and high porosity). More specifically, the employed chemical activation technique significantly increased the surface area from 565.09 m2/g for raw bamboo sawdust carbon (BSC) to 1158.05 m2/g for CAC. In the batch CIP adsorption system, CAC showed excellent CIP removal efficiency (96%) compared to BSC efficiency (45%). The parameters of CIP adsorption process, such as initial CIP concentration, pH, adsorbent dose, and contact time, were studied and found to have a significant effect on CIP removal from water. The optimal CIP removal (96%) was obtained at CAC dose (0.5 g/L), CIP initial concentration (20 mg/L), pH (7.5), and contact time (46 min). The kinetic data of single component CIP adsorption was well described by the pseudo-second-order model (R2 = 0.999), and both Langmuir (R2 = 0.994) and Freundlich (R2 = 0.972) models provided the best fit for the isotherm data. On the other hand, the single component batch adsorption of ACM resulted in 99.6% ACM removal from water using CAC under optimal conditions of ACM (20 mg/L), CAC (0.5 g/L), contact time (90 min), and pH (8). In this case, the kinetic study revealed that the ACM adsorption process followed the pseudo-second-order kinetic model (R2 = 0.999). On the other hand, the isotherm experimental data were best described by the Langmuir (R2 = 0.987) and Freundlich (R2 = 0.968) models. These results suggest that the adsorption of single component ACM and CIP was mainly controlled by chemisorption process. Moreover, the single component removal of ACM and CIP isotherm analysis revealed that ACM and CIP adsorption onto the CAC was monolayer adsorption onto the heterogeneous surface. The reusability study depicted that CAC can be successfully reused for five consecutive adsorption-desorption cycles in the batch adsorption of single component ACM and CIP. The single component ACM and CIP adsorption study exhibited a greater removal capacity for ACM (192.43 mg/g) than CIP (70.95 mg/g), as predicted by the non-linear Langmuir isotherm model. The competitive Langmuir isotherm model, employed for the simultaneous adsorption of ACM and CIP, predicted a maximum adsorption capacity of 125.31 mg/g for ACM and 65.44 mg/g for CIP. In this regard, the adsorption capacity ratio (qm, binary/qm, single < 1) suggests an antagonistic behavior of these pollutants when they co-exist in the same water matrix. On the other hand, the binary component adsorption of ACM and CIP was best described by the pseudo-second-order kinetic model, indicating that the chemisorption process mainly controlled the adsorption process. Under optimal conditions (inlet ACM/CIP concentration = 10 mg/L, flow rate = 1.5 mL/min and adsorbent loading = 100 mg), the fixed-bed column study showcased the maximum bed capacity of ACM (172.48 mg/g) and CIP (147.67 mg/g), with the highest respective removal efficiency of 44.23% and 37.86% in the binary component adsorption system in . However, the single component column adsorption system achieved a higher removal efficiency of 65.83% (ACM) and 42.59% (CIP). The EO process was also employed for the simultaneous degradation of ACM and CIP in the water. The central composite design (CCD) was employed for optimizing the EO process, and optimal conditions for current density (44 mA/cm2), pH (5.5), contact time (80 min) and initial pollutant concentration (20 mg/L) were obtained. Under these conditions, a removal of 94.5% for ACM and 92.7% for CIP was achieved. The EO process resulted in 65% total organic carbon (TOC) and 90.4% chemical oxygen demand (COD) removal at 240 min under optimal conditions. The EO kinetic study revealed that the degradation of ACM and CIP followed pseudo-first-order kinetics. The coupled process (EO+adsorption) optimization using the Box-Behnken Design (BBD) of the response surface methodology (RSM) technique provided optimal operating conditions for current density (22 mA/cm2), pH (5.5), EO time (40 min), adsorbent dose (0.1g/L) and adsorption time (60 min). Under these conditions, remarkable removal of pharmaceuticals (> 99.9%) and > 99% of TOC and COD were achieved when the EO time was extended to 120 min. Furthermore, the coupled process was employed for the simultaneous removal of multiple pharmaceuticals (20 mg/L of ACM+CIP+ATN (atenolol)+AMX (amoxicillin)) from water under optimal conditions. On top of that, the effect of water matrix on the target pharmaceuticals removal performances of EO, adsorption and EO+adsorption was investigated. These results show that the single processes (EO and adsorption) are highly sensitive to the water matrix compared to the coupled (EO+adsorption) process. Consequently, coupling the EO process with adsorption proved to be effective in addressing the influence of the water matrix, which substantially affected the removal efficiencies of the single processes. Overall, the coupled process demonstrated remarkable performances in single (ACM or CIP), binary (ACM+CIP), multiple pharmaceuticals (ACM+CIP+ATN+AMX), and oxidation by-products removal from diverse water matrices. Therefore, the EO+adsorption can serve as a promising treatment technique for the remediation of recalcitrant and ubiquitously detected pharmaceutical contaminants, such as ACM, CIP, ATN, and AMX from water.
Description
Keywords
Enhanced Removal, Pharmaceutical Contaminants, Water Using Electrochemical, Oxidation Coupled with Adsorption Process